Identification of N-terminal autodigestion target site in subtilisin ALP I

Autodigestion of subtilisin ALP I (ALP I), secreted from the alkalophilic B acillus sp. NKS-21 and its predicted amino acid sequence having about 60% i dentity with other alkaline subtilisins, was examined under alkaline condit ions, At the alkaline pH of 12, ALP I was rapidly degraded, and almost no b reakdown products were detectable. However, by incubating ALP I at 5 degree sC for an extended time, a couple of specific peptides (26.7 kDa and 25.6 k Da) were accumulated. Each of them was purified and amino acid sequences of these fragments were found. Both peptides appeared to start at Gly-19 of t he mature sequence of ALP I.